The gene/environment interactions that influence the development of allergic sensitisation and disease commence early in foetal life. The health, nutrition and environmental exposures of the mother during pregnancy have a profound effect not only on immune ontogeny but also on airway form and function. However, the influences on susceptibility to allergy may be different to those that affect manifestations of allergic disease such as asthma. A number of macro- and micro-nutrients have effects on either the risk of allergic sensitisation or allergic disease or both. Understanding the interactions will facilitate the identification of nutritional supplements which might lead to interventions which will prevent disease.